|Publication number||US7889208 B1|
|Application number||US 10/804,434|
|Publication date||Feb 15, 2011|
|Priority date||Oct 2, 2000|
|Also published as||US6731298|
|Publication number||10804434, 804434, US 7889208 B1, US 7889208B1, US-B1-7889208, US7889208 B1, US7889208B1|
|Inventors||Henry P. Moreton, John Erik Lindholm, Matthew N. Papakipos, Harold Robert Feldman Zatz|
|Original Assignee||Nvidia Corporation|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (17), Non-Patent Citations (5), Referenced by (3), Classifications (14), Legal Events (3)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The present application is a continuation of an application filed Oct. 2, 2000 under application Ser. No. 09/678,111, now U.S. Pat. No. 6,731,298 which is incorporated herein by reference in its entirety for all purposes.
The present invention relates to computer graphics, and more particularly to mapping of depth values during computer graphics processing.
Generally, bump and texture mapping are processes where basic contours of an object are expressed as a polygon in a modeling process and real world map data is used for a rendering process. During the course of bump and texture mapping, a color calculation is performed to incorporate colors onto an object in display coordinate space. This object with the colors is then displayed on a display device.
During bump mapping, the aforementioned normal values are modified based on a bump map algorithm using the bump mapping information, as indicated in operation 102 of
Thereafter, lighting operations such as shading or the like are performed on the pixel data using the perturbed normal values instead of the original normal values, as indicated in operation 104. This method gives the appearance of bumps and depressions in the surface. Also at this time, the color calculation may be carried out in order to enhance the color of the pixel.
While the foregoing bump and texture mapping techniques feature the unevenness of a surface and enhance the color of a pixel, they do not work well to reflect any unevenness in shadows cast by or onto the bumpy surface. Further, there are also limitations as to the interaction of geometric objects. These drawbacks are mainly due to the fact that conventional bump and texture mapping processes have no impact on the z-value of the pixel.
There is thus a need for a texture/bump mapping scheme during graphic processing that overcomes these drawbacks for providing a more realistic rendered image.
A system, method and computer program product are provided for computer graphics processing. In use, a value is modified based on an algorithm. An operation is subsequently performed on pixel data taking into account the modified value.
The foregoing and other aspects and advantages are better understood from the following detailed description of a preferred embodiment of the invention with reference to the drawings, in which:
Bump and texture mapping are techniques to add more realism to synthetic images. Texture mapping adds realism by attaching images to geometric surfaces. Bump mapping adds per-pixel surface relief shading, increasing the apparent complexity of the surface. Surfaces that should have associated fine grain details, small-scale geometric features, roughness, etc. are good candidates for bump mapping.
A bump map is an array of scalar or vector values that represents an object's features on a small scale. A custom renderer is used to map these height values into changes in the local surface normal. These perturbed normals are combined with the surface normal, and the results are used as inputs to a lighting equation at each pixel. In addition to using perturbed normals in such a manner, the present invention further modifies depth-values to enhance graphics processing. It should be noted that one embodiment of the present invention may optionally modify z-values using a related, but separate map of scalar displacements, similar to traditional bump maps.
The bump mapping module 340 and memory 320 work together to store bump maps by storing a normal vector in a texture map. Conventional RGB values describe a normal vector relative to a coordinate frame defined at the vertices of the primitive, i.e. triangle. Three vectors including tangent, normal, and binormal vectors are interpolated, and the vector read from the texture map is then rotated by taking its dot product with each of the interpolated vectors, in turn. The result is the bump mapped normal which may be then processed by the lighting and coloring module 310 in a conventional manner.
Thereafter, the depth-value is modified based on a depth-component of an algorithm. See operation 402. Such algorithm may include a bump map algorithm, texturing algorithm, etc. It should be noted, however, that any other desired algorithm may be utilized.
An operation is subsequently performed on the pixel data taking into account the modified depth-value, as indicated in operation 404. In one embodiment of the present invention, the operation may include a lighting operation. It should be noted, however, that the operation may take any form such as a hidden surface (z-test) calculation, shadow map operations, etc. A hidden surface calculation may determine visibility of various objects or portions thereof on the display device. Shadow map operations determine visibility with respect to another viewpoint such as a light source, thus permitting shadowing. During use, the foregoing operations function in a conventional manner, with the exception of using a modified depth-value as opposed to the original depth-value.
The technique for modifying or correcting the depth-values can be derived by perturbing eye-space value pe using Equation #1.
p′ e =P e +Δn e Equation #1
Perturbed eye-space value p′e may then be run through a conventional projection transform, Tproj, associated with a viewing transformation that transforms the depth values from eye space to clip space. Clip-space zc and wc are thus extracted.
Thereafter, zc and wc are modified rendering z′c and w′c which are defined by Equations #2.
z′ c =z c+Δ(nĚT proj)
w′ c =w c+Δ(nĚT proj) Equations #2
To perform per pixel calculation, zc and nĚTproj are iterated, and the value of Δ is read from a texture map. In some cases, bump mapping may be used in conjunction with displacement mapping. The displacement mapping may occur at one level of detail and filtering. Since the z-texture contains total displacements, there may be a mechanism to take this partial (filtered) displacement into account. In such a situation, the vertices of the triangle may have already sampled the bump map once, and that earlier displacement may be subtracted from Δ in Equations #2. The result is set forth in Equations #3.
z′ c =z c+ΔB(nĚT proj)−ΔD(nĚT proj)
w′ c =w c+ΔB(nĚT proj)−ΔD(nĚT proj) Equations #3
The values ΔD are per vertex displacements already applied. The values ΔB are values read in from the z-texture map.
It should be noted that the final depth value used and stored in the frame buffer may be computed by taking zc/wc with some appropriate scale and bias to place it in window coordinates. Further information regarding this chain of transformations may be found in the OpenGL« specification. Further, it should be understood that modifying the depth value may allow the lighting operation to display the interaction of displayed objects. Further, the modified depth value may allow the lighting operation to display bumpy shadows when applied to a typical shadow algorithm.
The present embodiment thus permits the per-pixel adjustment of the depth value of a polygon. The depth value of a polygon normally varies linearly, i.e. the polygon is planar. The present embodiment represents a mechanism by which the depth value is adjusted using a map, and the amount of adjustment is proportional/correct based on pre-projection coordinates. In effect, the modification has the projection transformation applied to it. It should be noted that this technique may be applied in contexts beyond bump mapping.
While various embodiments have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of a preferred embodiment should not be limited by any of the above described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.
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|U.S. Classification||345/584, 345/587, 345/426, 345/586, 345/583, 345/585, 345/582|
|International Classification||G09G5/00, G06T15/20, G06T11/00|
|Cooperative Classification||G06T11/001, G06T15/04|
|European Classification||G06T15/04, G06T11/00C|
|Oct 1, 2010||AS||Assignment|
Owner name: NVIDIA CORPORATION, CALIFORNIA
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:MORETON, HENRY P.;LINDHOLM, JOHN ERIK;PAPAKIPOS, MATTHEWN.;AND OTHERS;SIGNING DATES FROM 20010226 TO 20010305;REEL/FRAME:025080/0698
|May 10, 2011||CC||Certificate of correction|
|Jul 16, 2014||FPAY||Fee payment|
Year of fee payment: 4